Document scanners generally use an imaging or optical recognition device. In use, the device is placed over the document to be scanned and any image on the document is converted by the device into electrical impulses and stored. After the document has been viewed the stored image can be fed into a suitable printer and the document re-created.
Charge coupled device (CCD) arrays, are commonly used as the imaging or optical recognition device. Such CCD arrays are cheap, have good resolution and are readily available but because of cost and difficulty in manufacturing, are generally less than 5 inches in length and 1/2 inches in width.
The use of such an array; in a scanner, requires either; a vertical traversal of the array down the length of the sheet being scanned to capture a vertical strip of the document, followed by a horizontal movement of the array so that the next adjacent vertical strip of the document can be scanned and captured; or a horizontal traversal of the array across the width of the sheet being scanned to capture a horizontal line of the document, followed by a vertical movement of the array so that the next adjacent horizontal line of the document can be scanned and captured.
In both cases the procedure requires the taking and storing a plurality of images which must then be matched, aligned and reassembled.
Many good, inexpensive, mechanical arrangements exist for accurately traversing the optical imaging device down the length or vertical dimension of the document so that accurate matching of the re-created images can be achieved. However, problems are found in the matching of the images in the horizontal dimension of the document, especially if the scanned document is skewed with respect to the horizontal orientation of the array, for the re-creation of error free images requires an alignment accuracy, between each of the array's horizontal position, of one pixel which is typically between 0.0016 and 0.00042 inches on the surface being scanned. Good, inexpensive, mechanisms that will achieve this required accuracy for horizontal positioning of the array are not available.
In an, attempt to avoid the horizontal traversing problems discussed above, CCD arrays have been made wide enough to scan a desired page. Such wide arrays have the advantage of scanning, for example, an entire line in a single pass thus avoiding the problem of horizontal stitching of the image but have the disadvantage of increased cost and, in the case of wide engineering or architectural drawings, decreased resolution, i.e., less than 200 dots per inch (DPI).
One attempt to avoid these problems is to physically align a plurality of small arrays so that the line of arrays will capture, as a single image, a horizontal strip of a document. By using smaller arrays, good image resolution is realized but again the re-creation of error free images requires, between each of the arrays in the line, an alignment accuracy of a few pixels. Such an accurate alignment, in such equipment, is possible to achieve in a laboratory but virtually impossible to maintain when the scanners are used in the commercial world. Shock, mechanical movement of the scanners, or etc. that the equipment may be subject to, during actual use, will cause the arrays to become misaligned and the required accuracy lost.
Accordingly, the art has been searching for a scanner using a small, high resolution CCD array that will accurately and easily re-create an error free reproduction of a scanned image of any size.